Mechanism for applying high radial force in less-elastic medical devices

ABSTRACT

A biodegradable device capable of producing a high radial force is described. Such a force will be created in devices made of relatively inelastic materials that are to be deployed to the vasculature or a body cavity in a patient. As the halves of the devices move together subject to a longitudinal force, at the point where they are in contact and unable to move closer together in the longitudinal direction, a radial force is created. The devices may have a tension element that assists in bringing the device halves together and which may partially and optionally remain within the body of the device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application from U.S. Non-Provisionalapplication Ser. No. 14/666,728, filed on Mar. 24, 2015, which claimsthe benefit of U.S. Provisional Patent Application No. 61/971,836, filedon Mar. 28, 2014, the entire contents of which is hereby incorporated byreference.

BACKGROUND

The present invention relates to medical devices. More particularly, theinvention relates to a device made from a less-elastic or biodegradablematerial that is capable of producing a relatively large radial force inorder to prevent device migration and/or maintain patency in a bodyvessel.

Filtering devices are percutaneously placed in body vessels of a varietyof medical patients, including but not limited to trauma patients,orthopedic surgery patients, neurosurgery patients, or in patientshaving medical conditions requiring bed rest or non-movement. Duringsuch medical conditions, the need for filtering devices arises due tothe likelihood of thrombosis in the peripheral vasculature of patientswherein thrombi break away from the vessel wall, risking downstreamembolism or embolization. For example, depending on the size, suchthrombi pose a serious risk of pulmonary embolism wherein blood clotsmigrate from the peripheral vasculature through the heart and into thelungs. In some cases, a filtering device can be deployed in the venacava of a patient when, for example, anticoagulant therapy iscontraindicated or has failed.

Typically, filtering devices are permanent implants, each of whichremains implanted in the patient for life, even though the condition ormedical problem that required the device has passed. However, it can bedesirable to remove unneeded implants when the medical risk has passed.

In some cases, filters have not been considered removable from a patientdue to the likelihood of endotheliosis of the filter or fibrous reactionmatter adherent to the endothelium during treatment. After deployment ofa filter in a patient, proliferating intimal cells begin to accumulatearound the filter struts which contact the wall of the vessel. After alength of time, such ingrowth prevents removal of the filter withoutrisk of trauma, requiring the filter to remain in the patient.

Even in cases where removal of the implant or device is possible, asecond surgical procedure and the attendant risks can be undesirable. Assuch, removal of the device, even when possible, is sometimes notelected.

Medical devices, including filtering devices, can be made frombiodegradable materials. These devices have the advantage of functioningfor a limited time and then slowly get absorbed by the patient's body,obviating a second surgery for removal of the device. However, unlikepermanent devices made from elastic materials like spring steel orshape-memory metals, devices made from biodegradable materials can lackmechanical properties and in some cases make suboptimal contact withvessel walls, thereby risking migration.

It is desirable to use a medical device made of a biodegradable materialwhich can also produce a strong radial force against the wall of a bodyvessel.

SUMMARY

According to a first aspect of the present invention, a medical devicefor implantation in a body vessel is provided comprising a first colletcomprising a first tube and a first cap, the first tube having a firsttube end and extending to a second tube end, and a lumen formed throughthe first tube end to the second tube end, the first cap having aninterior surface and being attached to the first tube end; a firstdevice half having a proximal end and a distal end opposite the proximalend and defining a longitudinal axis therethrough, the first device halfcomprising a plurality of struts having a first arm and a second armconnected to the first arm, each first arm having a first end disposedat the proximal end of the first device half, the first arm extendingangled away from the longitudinal axis to a second end, each second armhaving a third end connected to the second end of the first arm andextending proximally and substantially parallel to the longitudinal axisto a fourth end, a locking element being disposed on at least one firstarm, the second tube end of the first tube being attached to the firstarms at the proximal end so that the first ends are disposed within thelumens of the first tube; a second collet comprising a second tube and asecond cap, the second tube having a first tube end and extending to asecond tube end, and a lumen formed through the first tube end to thesecond tube end, the second cap having an aperture formed therethroughand being attached to the first tube end; a second device half having aproximal end and a distal end opposite the proximal end and defining alongitudinal axis therethrough, the second device half comprising aplurality of struts having a first arm and a second arm connected to thefirst arm, each first arm having a first end disposed at the distal endof the second device half, the first arm extending angled away from thelongitudinal axis to a second end, each second arm having a third endconnected to the second end of the first arm and extending distally andsubstantially parallel to the longitudinal axis to a fourth end, alocking element being disposed on at least one first arm, the secondtube end of the second tube being attached to the first arms at thedistal end so that the first ends are disposed within the lumens of thesecond tube; and a tensioner having a first end and a second end, thefirst end of the tensioner being attached to the interior surface of thefirst cap, the tensioner extending to the second end through theaperture of the second collet.

In another embodiment, a medical device is provided comprising a firstcollet comprising a first sleeve and a first cap, the first sleevecomprising a tube having a first tube end, a second tube end, and alumen formed therethrough, the first cap having an interior surface, thefirst cap being attached to the first tube end of the first sleeve; afirst device half having a longitudinal axis and comprising a pluralityof struts, each strut comprising a first arm having a first end and asecond end, the first arm extending substantially parallel to thelongitudinal axis and from the first end to the second end, the firstends of the first arms being disposed through the second tube end andwithin the lumen of the first sleeve and attached substantiallycircumferentially about the interior surface of the first cap, eachstrut having a pair of secondary arms each having a first end and asecond end, the first end of a secondary arm being attached to thesecond end of a first arm, the secondary arms being arranged to form asubstantially cylindrical device half; a second collet comprising asecond sleeve and a second cap, the second sleeve comprising a tubehaving a first tube end, a second tube end, and a lumen formedtherethrough, the second cap having an interior surface and an apertureformed therethrough in fluid contact with the second lumen, the secondcap being attached to the first tube end of the second sleeve; a seconddevice half opposite and in alignment with the first device half, thesecond device half having a longitudinal axis and comprising a proximalend and a distal end, the second device half comprising a plurality ofstruts, each strut comprising a first arm having a first end and asecond end, the first arm extending substantially parallel to thelongitudinal axis and from the first end to the second end, the firstends of the first arms being disposed through the second tube end andwithin the lumen of the second sleeve and attached substantiallycircumferentially about the interior surface of the second cap, eachstrut having a pair of secondary arms each having a first end and asecond end, the first end of a secondary arm being attached to thesecond end of a first arm, the secondary arms being arranged to form asubstantially cylindrical device half; and a tensioner having a firstend and a second end, the first end of the tensioner being attached tothe interior surface of the first cap, the tensioner extending to thesecond end through the aperture of the second collet.

According to another aspect of the present invention, there is provideda medical device comprising a first collet comprising a first sleeve anda first cap, the first sleeve comprising a tube having a first tube end,a second tube end, and a lumen formed therethrough, the first cap havingan interior surface, the first cap being attached to the first tube endof the first sleeve; a first device half having a longitudinal axis andcomprising a plurality of struts, each strut comprising a first armhaving a first end and a second end, the first arm extendingsubstantially parallel to the longitudinal axis and from the first endto the second end, each strut having a pair of secondary arms eachhaving a first end and a second end, the first end of a secondary armbeing attached to the second end of a first arm, the second ends of thesecondary arms being disposed through the second tube end and within thelumen of the first sleeve and attached substantially circumferentiallyabout the interior surface of the first cap, the first arms beingarranged to form a substantially cylindrical device half; a secondcollet comprising a second sleeve and a second cap, the second sleevecomprising a tube having a first tube end, a second tube end, and alumen formed therethrough, the second cap having an interior surface andan aperture formed therethrough in fluid contact with the second lumen,the second cap being attached to the first tube end of the secondsleeve; a second device half opposite and in alignment with the firstdevice half, the second device half having a longitudinal axis andcomprising a plurality of struts, each strut comprising a first armhaving a first end and a second end, the first arm extendingsubstantially parallel to the longitudinal axis and from the first endto the second end, each strut having a pair of secondary arms eachhaving a first end and a second end, the first end of a secondary armbeing attached to the second end of a first arm, the second ends of thesecondary arms being disposed through the second tube end and within thelumen of the second sleeve and attached substantially circumferentiallyabout the interior surface of the second cap, the first arms beingarranged to form a substantially cylindrical device half; and atensioner having a first end and a second end, the first end of thetensioner being attached to the interior surface of the first cap, thetensioner extending to the second end through the aperture of the secondcollet.

Further aspects, features, and advantages of the invention will becomeapparent from consideration of the following description and theappended claims when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are described below, byway of example only with reference to the accompanying drawings inwhich:

FIG. 1A is a side view of a biodegradable device filter half inaccordance with one embodiment of the present invention;

FIG. 1B is a side view of two biodegradable device filter halves forminga single filter device in accordance with one embodiment of the presentinvention;

FIG. 2A-2D are side views of a biodegradable device filter beingdeployed in accordance with one embodiment of the present invention;

FIG. 3 is a view of three struts meeting in accordance with oneembodiment of the present invention;

FIG. 4A-4B are views of strut configurations in accordance with furtherembodiments of the invention;

FIG. 5A-5B are perspective views of a collet in accordance with oneembodiment of the present invention;

FIG. 6A-6B are views of forking struts in accordance with anotherembodiment of the present invention;

FIG. 6C-6D are views of device halves comprising forking struts inaccordance with another embodiment of the present invention

FIG. 6E is a view of two device halves coming together to form a fulldevice, the forked ends of the struts being placed within the collet, inaccordance with another embodiment of the present invention; and

FIG. 6F is a view of two device halves coming together to form a fulldevice, the non-forked (or single) ends of the struts being placedwithin the collet, in accordance with another embodiment of the presentinvention.

DETAILED DESCRIPTION

It is to be understood that the figures are schematic and do not showthe various components to their actual scale. In many instances, thefigures show scaled up components to assist the reader.

In this description, when referring to a deployment assembly or amedical device, the term distal is used to refer to an end of acomponent which in use is furthest from the surgeon during the medicalprocedure, including within a patient. The term proximal is used torefer to an end of a component closest to the surgeon and in practice inor adjacent an external manipulation part of the deployment or treatmentapparatus.

“Substantially” or derivatives thereof as used herein will be understoodto mean significantly or in large part. The terms “substantially” or“about” used herein with reference to a quantity includes variations inthe recited quantity that are equivalent to the quantity recited, suchas an amount that is equivalent to the quantity recited for an intendedpurpose or function.

A component which is “angled away” from another component may or may notshare a vertex with the component from which it is angled away. Theangle formed when a component is “angled away” from another component isa non-zero angle; that is, the component which is angled away does notrun parallel to, or entirely overlie, the component from which it isangled away.

An example of a medical device half made from a biodegradable materialis illustrated in FIG. 1A. Device half 10 comprises a plurality ofstruts 12 which can have first arm 15 and second arm 17. In theembodiment illustrated, the device half comprises four struts, but adevice with two struts, three struts, five struts, six struts, eightstruts, ten struts, twelve struts, or another number of struts is alsopossible in accordance with the principles of this invention.

The device half 10 may have a substantially conical shape. A conicalshape has an open end and an apical end. In this case, the apical endwould comprise the collet 14 at which the struts 12 converge. The collet14 surrounds a first end of each strut 12.

Each first arm 15 has a first end and a second end. The first end meetsand is attached to, or disposed within, collet 14. Such attachment maybe fixed attachment, or unfixed attachment in which the end of the strutis disposed within the collet and held there by radial forces, ratherthan by a securing mechanism such as adhesive, glue, soldering, or thelike. The second end of first arm 15 is attached to second arm 17 atstrut arm junction 13. In one embodiment, the overall shape of strut 12is a V-shape or a triangular shape. Collet 14 has a cap portion 16.

In another embodiment, the struts 12 comprise only a single strut armsuch as first arm 15.

In one embodiment of the device, the struts 12 act to filter emboli inthe vasculature of a patient who is being treated. The first arm 15 orthe second arm 17, or both, may be in contact with a vessel wall of thepatient.

In one aspect, the device comprises two device halves. Turning now toFIG. 1B, two device halves 10 and 11 interacting with one another arearranged to form the full device 20. The device 20 has a proximal end 21and a distal end 22, although in many cases the device is symmetricaland the proximal end 21 may be implanted in the patient distally and thedistal end 22 may be implanted in the proximal direction. Impartingdirectionality to the device 20 may be tensioner 18. The tensionerelement 18 is attached to a first collet 14, in some embodiments oncollet head 16. The collet may comprise a head or cap portion attachedto a sleeve, which is hollow tube. The cap portion may simply cover andclose the open end of the tube or sleeve of the collet. The cap portionhas an interior, disposed facing the lumen of the tube, and an exterioropposite the interior. The interior of the cap provides a good surfacefor the attachment of a tensioner. In some cases the tensioner may beattached by an adhesive. In another embodiment, the cap may have a loopformed on it on the interior side, and the tensioner may be threadedthrough the loop and tied to it. In some embodiments, the tensioner 18overlies the longitudinal axis 23 of the device 20. In some embodiments,the tensioner 18 passes through a hole 33 that is formed through thesecond collet of device 20. The first collet and the second collet areprovided in one embodiment in opposite orientations to one another; thatis, the head or cap portions of the collets represent the extremeproximal and distal ends of the device 20.

In one embodiment, the distal end 21 of the device 20 is the end where acollet is attached in a fixed fashion to the tensioner 18, and theproximal end is the end where the tensioner 18 passes through a hole orchannel 33 which is formed or bored through a collet.

The points where first device half 10 and second device half 11 comeinto contact during deployment are known as locking zones 25. In theembodiment of FIGS. 1-2, the locking zones 25 are made possible by thepresence of locking bumps 19. The general way in which the deviceprovides a radial force, which allows for better patency and increasedcontact with the vessel wall, is that the tensioner 18 is pulled inthrough the hole 33 in the second collet 14 at the proximal device end22 and as a force is applied along the longitudinal axis 23, the devicehalves come together. In one embodiment, this is due to the first devicehalf 10, which is fixedly attached to the tensioner 18, moves in theproximal direction. The device halves 10 and 11 then contact one anotherat their locking zones 25 via locking bumps 19. At this point, thedevice halves 10 and 11 can no longer move together along thelongitudinal axis 23. As a result, the force applied in the longitudinaldirection results in a compression of the device halves 10 and 11 asthey experience a greater force against one another. This causes anexpansion in the radial direction, substantially normal to thelongitudinal axis. Such radial expansion can occur either with orwithout a substantial change in the length of the device along alengthwise dimension (that is, parallel to the longitudinal axis of thedevice 20.) This, in turn, provides an increased amount of contact withthe vessel wall, and therefore better patency and higher radial force ofthe device within the vasculature of the patient to be treated.

The shape of a strut 12 can be substantially V-shaped or triangular.Optionally, the strut 12 may have a first portion which is substantiallyparallel to the longitudinal axis 23. A strut 12 may also have anoptional second portion which is substantially parallel to thelongitudinal axis. These first and second portions may be substantiallyparallel to one another. The first portion may have the ability to moreconveniently be fit into a collet 14 which has a central lumen 38. Thesecond portion can provide a relatively small area of greater contactwith a vessel wall during initial deployment.

Optionally, the strut 12 has a locking bump 19. This locking bumpprovides a greater area of contact between the device halves 10 and 11.The locking bump can be employed in many designs of a device half butparticularly in embodiments wherein the struts 12 consist of only asingle arm.

FIG. 2 shows how the device halves 10 and 11 can come together to formdevice 20 in a method of deployment. The method of capturing thrombi ina body vessel may comprise the steps of deploying a filter such that anarm of a strut is positioned against the internal wall of a vessel, thefilter having a first device half and second device half which can moveindependently of each other along the longitudinal axis of the device.In one embodiment, the proximal (closest to the operator) device halfhas been more securely engaged to the internal wall of the vessel thanhas the distal device half. The first half approaches, then contacts,the second device half. In one embodiment, portions of the first devicehalf may even slide past parts of the second device half.

The first device half and the second device half each have a lockingfeature 19 on a portion of some of their struts. In depictedembodiments, the locking features 19 are shown on the first arms 15. Thelocking features of the device halves engage when the device halves arepushed or pulled together, such as when a tensioner fixed to thedistal-most device end is pulled proximally. The medical device is ableto expand in a radial direction after the locking features have engagedand upon application of further force which would otherwise push thedevice halves toward one another, but because the halves areinterlocked, a force substantially normal to the direction of pulling isgenerated.

In one embodiment the tensioner 18 can be broken when a sufficientpulling force is applied thereto, with a shortened tensioner portionremaining connecting the first collet to the second collet. In general,the second collet will have a notch, a hole, or another similar featureinto which the tensioner 18 can be positioned and secured. Then afurther force can be applied, such as pulling against a wall of thecollet, or simply pulling more forcefully on the tensioner 18 to snapit. In some embodiments, a knot may be tied in the tensioner 18 so thatit can more easily be held by the notch or similar tensioner-retainingfeature of the collet. In another embodiment, the tensioner may simplybe thicker at this point, or may have another component, possibly madeof a different material, which will catch in the notch of the secondcollet.

FIG. 2A shows how the device halves are spaced apart after initialdelivery. A suitable deployment apparatus, such as an introducingcatheter, optionally employing a wire guide, has been inserted into abody cavity of a patient to be treated. In some embodiments, thisinsertion is percutaneous. The device halves 10 and 11 are eitherentirely separate from one another or only in minimal contact with oneanother in this step. The tensioner 18 is seen attached to first collet14 at the proximal end 21 of device half 10 and passing through anaperture of the second collet, which has as part of it tensioner point24 at or near a hole or channel 33.

In FIG. 2B, the practitioner has applied a force 26 to the tensioner 18.In one embodiment, the tensioner 18 is long enough to pass through thedelivery assembly and be manipulated by the interventionalist (orpractitioner, physician, or surgeon.) In another embodiment, thetensioner 18 is has a shorter length but can be manipulated by theinterventionalist by using a tool, such as forceps, that are used inconjunction with the delivery assembly and either contact the tensioner18 within the delivery assembly or in the vasculature of the patient. Atthis step, the force 26 causes the two device halves 10 and 11 cometogether and begin to engage with one another.

FIG. 2C shows the two device halves 10 and 11 fully engaged with oneanother as a result of the continued application of force 26. Thelocking zones 25 are now formed. In the embodiment illustrated, theselocking zones 25 are initially strut arm junctions 13 and the portionsof the opposite device half that the junctions 13 contacts. As the force26 continues to act on the tensioner 18 and bring the device halves 10and 11 in increased contact with one another, the lock zones 25 canbecome as extensive as the entire lengths of the struts 12, includingthe majority or entirety of first arms 15 and second strut arms 17. Asshown in FIG. 2C, the device 20 has a first width dimension 27 and afirst device length 28. The first width 27 is substantially the samewidth at this point in the method as at was in the step of FIG. 2A, butthe first device length 28 has decreased as the force 26 has brought thedevice halves 10 and 11 together.

FIG. 2D shows the two device halves fully engaged with one another.After the locking zones 25 have met to their fullest extent, additionalforce 26 from continued pulling toward the interventionalist ontensioner 18 causes the device halves 10 and 11 to apply contact forcesto one another such that the radial force 35 is exerted. This causes thedevice to expand to second device width 29, which is greater than firstwidth 27. The second device length 30 may be less than first devicelength 28, or it may be substantially equal to (that is, not detectablydifferent from) first device length 28. The device 20 now contacts thevessel wall and maintains patency of the device due to radial force 35which continues to push the device outward relative to the longitudinalaxis 23 of the device 20 while and after the device is implanted.

When the device 20 is fully deployed, the tensioner 18 can have a numberof outcomes. The tensioner 18 can be made of a biodegradable material ora non-biodegradable substance. If the tensioner 18 is made of anon-degradable material, it must be removed entirely from the patient.This can be achieved by making the contact between the collet to whichit is fixed at the proximal end 21 sufficiently strong to allow thedevice halves 10 and 11 to be pulled together and fully deployed butsufficiently weak to break this connection when the device has achievedits maximum patency configuration.

Contrarily, if the tensioner 18 is made of biodegradable material, itmay be simply cut by the interventionalist and left within the patientto safely degrade. Alternatively, the tensioner contact zone 24 of thecollet 14 may be notched, the notch having a width that is substantiallysimilar to the width of the tensioner 18, that the tensioner can bepositioned within. If the interventionalist makes a pulling motion at anangle to the longitudinal axis 23, the tensioner 18 will catch in thenotch at the contact zone 24 and snap at that point. As a result, thetensioner 18 will have a shorter length, stretching only from proximalend 21 to distal end 22 of the device 20. The tensioner 18 will continueto force device halves 10 and 11 together and this force may assist inmaintaining patency of the device 20 and preventing migration.

The tensioner 18 may be made of polycaprolactone (PCL). PCL is abiodegradable polyester which can be manufactured into a stretchablefilament or strand. The tensioner may also be a copolymer of PCL and PLAin a predetermined ratio which will provide optimal stretchability andstructural integrity. Over the course of deployment, the tensioner 18will degrade, as will the remainder of the device.

FIG. 3 illustrates how the struts 12 come together in a differentembodiment of the device. The struts of device half 10 contact those ofdevice half 11. The first arms 15 and second arms 17 of the strut of onedevice half are in contact with those of the other half, along amajority or the entirety of their lengths. This ensures interlocking ofthe halves and increases the chances of the halves creating radialforce. In such an embodiment, the locking zone is represented by a largeportion of the device arms, and no locking bump is present. In apreferred embodiment, the number of struts on the first device half 10is equal to those of the second device half 11. In another embodiment,the first device half 10 has one more strut than device half 11, or onefewer. The interlocking triangular or V-shaped strut structure canprovide a device 20 suitable for filtration of emboli which issubstantially cylindrical in shape and suitable for maintaining patencyin a vessel.

FIGS. 4A and 4B show embodiments of struts in accordance with furtheraspects of the invention of the present disclosure. In FIG. 4A, strut 40has a pair of first strut arms 41 joined by triangular strut 42. Thestrut arms 41 meet triangular strut 42 at junctions 45. The triangularstrut has an open portion and opposite that a vertex 48. FIG. 4B shows asimilar configuration, but instead of junctions 45 being substantiallymidway down the length of strut arms 41, the junctions 45 at the ends offirst strut arms 41. This gives an overall M-shape to the struts.

The struts may be individually cut or formed from the material andinserted within the collet. Alternatively, the struts may be cut from atube of the material, such as by a laser.

FIG. 5 is an illustration of the collet in accordance with an embodimentof the invention. The collet 14 has a head portion 16 and an aperture orchannel 33 formed therethrough. Referring to FIG. 5B, the central lumen38 of the collet 14 can be seen. The central lumen 38 has a diameter,which should be wide enough to accommodate some or all of the first endsof the struts 12. Optionally, collet 14 may include slots 34, whichimpart some flexibility in order to adjust for small variations in thestruts that will be fit therein. The collet 14 should be made ofrelatively rigid material but also should be biodegradable.

The aperture of a collet, particularly a second collet, provides a spacefor the tensioner of a device to pass through. The interventionist pullsthe tensioner to first bring the device halves together and then bringthem into contact with one another, the device halves extending radiallyas an additional force is applied to the frame of the device by furtherpulling on the tensioner.

In FIGS. 6A and 6B, another embodiment of a strut is shown. The strut isforked or pronged. Strut 112 has an overall pronged shape, with a firstarm 114 having first end (or first arm first end) 110 and extending to asecond end (or first arm second end) at forking point 113. Two secondarystrut arms (or first secondary arm and second secondary arm) 115 extendfrom a first end (or first second arm end) at forking point 113 to asecond end (or second second arm end) at 111. The pronged strutstructures may take a U-shape as in FIG. 6A, or a V-shape as in FIG. 6B.In the embodiment of FIG. 6B, the second strut arms 215 meet at forkingpoint 213 at a sharp angle and then converge into first strut arm 214 atthe first end 210. In one embodiment, the second strut arms may insteadtake on an overall U shape, as the secondary arms run parallel to oneanother for much of their lengths but bend curvedly toward the forkingpoint.

FIGS. 6C and 6D show device halves 300 and 400 respectively whichillustrate one way in which the pronged struts of FIGS. 6A and 6B can bearranged in a device half. In the embodiment shown in FIG. 6C, thestruts are arranged such that the first ends of the primary struts areconstrained within the collet and the second ends of the secondarystruts are free.

In the embodiment of FIG. 6D, the struts may instead be arranged suchthat the second ends 215/115 are contained within an empty space orlumen of a cap or collet 316/416. The first strut arms 214/114 are freeand unconstrained by such a cap. Although four struts 212/112 areillustrated in these figures, it is possible to construct device halveswith 2, 3, 5, 6, 8, 10, 12, or another number of struts per device half.

FIGS. 6E and 6F show how the device halves of FIGS. 6C and 6D merge tobecome a single device. In the case of FIG. 6E, the first arms 212 areconstrained within the collets of the device halves and the secondaryarms have free ends. The device halves are positioned opposite oneanother. The device halves are arranged such that when the tensioner ispulled and the device halves merge, the secondary strut arms willinterlock, their forking points substantially aligning radially. In suchan arrangement the secondary strut arms will make contact eithersubstantially at the forking point, in the case of the U-shaped arms, oralong some or all of the length of the secondary strut arms, such as inthe V-shaped arms. In an embodiment where both device halves have thesame number of struts, one device half is rotated slightly in such a wayto facilitate such interlocking. In another embodiment, one device halfmay have one more forked arm than the one with which it pairs.

In the embodiment of FIG. 6F, the first strut arms 114 are notconstrained by the collet now fit within the collet of the oppositedevice half or, alternatively, move into place outside of the oppositecollet. As the device halves merge together, the second strut arms215/115 approach one another and meet at the forking points 213/113.When the forking points 213/113 collide and a longitudinal forcecontinues to be applied to the device by a tensioner element, an outwardradial force is created and the device expands radially as a result. Thetensioner element may be used as described above to lock the devices ofFIGS. 6E and 6F into place.

There are many modifications that could be made to the above-describedembodiment. Other ways of achieving the function may be envisaged. Forexample, instead of V-shaped struts, the struts may take on a closedtriangular shape, with an extra crossbar across the top of the V-shape.In another embodiment, the struts 12 may have a single straight leg andmay be formed with locking bumps at one or more places along the lengthsof the strut arms.

Referring now to materials for creating a biodegradable device, they canbe fabricated from biocompatible materials. The devices are to bedelivered with limited vessel trauma, and, in some embodiments, canpossess the ability to break down entrapped emboli.

Some biodegradable materials can comprise a matrix which expands upondelivery. The device must capable of withstanding in vivo pressures,such as those created by heartbeat, breathing, blood pressure, andgeneral movement of the patient in order to minimize movement. In somecases, the device 20 is capable of delivering thrombolytic agents in acontrolled fashion.

The devices such as filtration devices described herein generallycomprise one or more polymers. In some embodiments, at least one polymercan be an expandable polymer. Of particular interest are polymers thatcan be compressed as compression can impart the radial force 35 thatassists in maintaining position and patency.

Various suitable polymers can be used including, for example,polyethers, polyesters, polyurethanes, and mixtures thereof. Compressedpolymers are physically deformable or elastic such that they can besqueezed into a sheath or the like for delivery into a vessel of thepatient, such that the polymer expands following removal from thesheath.

In some embodiments, the device comprises a plurality of polymers in ablend and/or a plurality of monomers in a copolymer, which can be ablock copolymer.

Using a plurality of polymers includes the ability to introduceproperties of each individual polymer or of each monomer groupincorporated into a copolymer. In general, the expansion of the polymerand the corresponding device can occur spontaneously following theapplication of an appropriate stimulus. The appropriate stimulus can be,for example, contact with an aqueous fluid, release of constrainingforces, such as applied by a sheath, and/or heating to body temperature.

The expandable nature of some polymers allows the device 20 to conformto the patient's vessel. Thus, minor variation in the vessel size andshape along the extent of the device can be handled appropriately byminor variations in the expansion of the device at different locations.

Biodegradable polymers and their degradative byproducts should benon-toxic, capable of maintaining good mechanical integrity untildegraded, and capable of controlled rates of degradation. Suitablepolymers preferably do not elicit an immune response.

Degradation generally proceeds by hydrolytic processes. Factorscontrolling the rate of degradation include but are not limited tomolecular weight and hydrophobicity of the polymers. The degradationrate can depend on the location in the body.

One polymer that can be used exclusively or preferably as a copolymer ispolylactic acid (PLA). PLA can be processed by extrusion, injectionmolding, film or sheet casting, and spinning. Thus, construction ofstruts 12 can be achieved in a number of ways.

Another polymeric substance that can be employed ispoly(lactic-co-glycolic) acid (PLGA.) PLGA has been successful as abiodegradable polymer because it undergoes hydrolysis in the body toproduce the original monomers, lactic acid and glycolic acid. These twomonomers under normal physiological conditions, are by-products ofvarious metabolic pathways of the body. There is minimal systemictoxicity associated with using PLGA for drug delivery or biomaterialapplications. Depending on the ratio of lactide to glycolide used forthe polymerization, different properties of PLGA can be obtained. Thelactide to glycolide ratio dictates stiffness, degradation time,flexibility, and other properties. The higher the content of glycolideunits, the lower the time required for degradation. An exception to thisrule is the copolymer with 50:50 monomers' ratio which exhibits thefaster degradation (about two months). In addition, polymers that areend-capped with esters (as opposed to free carboxylic acid) demonstratelonger degradation half-lives.

The device can in some aspects be used to provide temporary filtration.However, as mentioned above, the ratio of lactide to glycolide can beadjusted to create a polymer that has a relatively long half-life afterdeployment. Short-term and long-term implants are envisioned in usingthese biodegradable implants.

Another class of material that can be used in the manufacture of adevice with the properties described herein is a biodegradablepolyurethane or polyurethaneurea. A biodegradable polyurethane can beformed in many ways. One type of monomer that can be used as a startingmaterial in the manufacture of a suitable polyurethane is anisocyanate-based molecule. One type of isocyanate is an aliphaticdiisocyanate, including but not limited to 1,4-butanediisocyanate,1,6-hexamethylene diisocyanate, 2,2,4-trimethyl hexamethylenediisocyanate, ethyl 2,6-diisocyanatohexanoate, methyl2,6-diisocyanatohexanoate, isophorone diisocyanate, and 1,4-cyclohexanediisocyanate. Polyols can also be used, including but not limited topoly(ethylene oxide), poly(tetramethylene oxide), poly(propylene oxide),poly(propylene oxide), poly(D,L-lactide), poly(epsilon-caprolactone),poly(glycolide), poly(propylene fumarate), and combinations thereof suchas poly(lactic acid-ethyleneglycol-co-lactic acid). Such polyurethanescan be formulated using chain extending molecules including but notlimited to ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol,1,2-ethanediamine, 1,4-butanediamine, 2-amino-1-butanol,2-hydroxyethyl-2-hydroxypropanoate,4-((1-(1-amino-2-phenylethoxy)ethoxy)methylcyclohexyl)methyl-2-amino-3-phenylpropanoate, 1,1-(hexane-1,6-diyl)bis(3-(2-hydroxyethyl)urea),ethane -1,2-diyl bis(3-(4-hydroxyphenyl)propanoate),bis(2-hydroxyethyl)phosphate, and bis(2-hydroxyhexyl phosphate.

The struts of the device could further include attachment aids in orderto maintain attachment to the vessel wall and patency of the device. Forinstance, small barbs could be attached to the periphery of the device.An advantage of including barbs that engage the vessel wall is that thebarbs not only assist in fixing the device in place, but also irritatethe vessel wall. This promotes restenosis, which in turn assists inproviding improved fixation of the device within the blood vessel, andimproved occlusion. The barbs could be relatively blunt in order toavoid piercing the vessel wall upon radial expansion. A purifiedextracellular matrix (ECM) material might be employed over some or allof the device in order to further encourage ingrowth of tissue into thedevice, thereby fixing it within the vessel.

The device could also serve to deliver a substance such as a drug to thearea in which it has been deployed. In one embodiment, the struts of thedevice are coated with a polymeric coating. The polymeric coating may beporous and a drug to be delivered may be in the pores. In anotherembodiment, the struts themselves may be impregnated with a drug, thedrug being released as the device degrades.

While the present invention has been described in terms of preferredembodiments, it will be understood, of course, that the invention is notlimited thereto since modifications may be made to those skilled in theart, particularly in light of the foregoing teachings.

The invention claimed is:
 1. A medical device for implantation in a bodyvessel, the medical device having a proximal end and extending to adistal end and defining a longitudinal axis therebetween, the medicaldevice comprising: a first device half comprising: a first colletcomprising a first tube and defining a lumen therethrough; and aplurality of struts, each of the plurality of struts comprising a firstarm and a second arm connected to the first arm, each first arm having afirst end and extending angled away from the longitudinal axis to asecond end, each second arm having a third end connected to the secondend of the first arm and extending proximally and substantially parallelto the longitudinal axis to a fourth end, a locking element beingdisposed on at least one first arm, each of the first ends of the firstarms being disposed within the lumen of the first tube; a second devicehalf comprising: a second collet comprising a second tube defining alumen therethrough; and a plurality of struts, each of the plurality ofstruts having a first arm and a second arm connected to the first arm,each first arm having a first end and extending angled away from thelongitudinal axis to a second end, each second arm having a third endconnected to the second end of the first arm and extending distally andsubstantially parallel to the longitudinal axis to a fourth end, alocking element being disposed on at least one first arm, each of thefirst ends of the first arms being disposed within the lumen of thesecond tube; and a tensioner having a first end and extending to asecond end, the first end of the tensioner being attached to the firstcollet, the tensioner extending to the second end through the secondcollet; wherein the locking elements of the first and second devicehalves are configured to engage one another.
 2. The medical device ofclaim 1 wherein the first device half and the second device half have aconical shape comprising an apical end and an open portion opposite theapical end, the second ends of the first arms being arrangedcircumferentially about the open portion.
 3. The medical device of claim2 wherein the first ends of the struts of the device halves converge atthe apical end of each conical shape.
 4. The medical device of claim 1wherein when the first device half and the second device half are movedlongitudinally together, the locking elements of the first device halfcontact the locking elements of the second device half to form a lockinginterface such that application of a force along a longitudinal axis ofthe first device half in the distal direction causes the device to exerta force radially outward therefrom.
 5. The medical device of claim 1wherein the struts comprise a polymer.
 6. The medical device of claim 5wherein the polymer comprises at least one of a biodegradable polyester,polyether, or polyurethane.
 7. The medical device of claim 1 wherein thefirst collet and the second collet each comprise a biodegradablepolymer.
 8. The medical device of claim 1 wherein the second colletfurther comprises a tensioner-retaining groove for retaining a portionof the tensioner.
 9. The medical device of claim 1, wherein the firsttube extends from a first tube end to a second tube end, and the firstcollet comprises a first cap at the first tube end.
 10. The medicaldevice of claim 9, wherein the first end of the tensioner is attached tothe first cap.
 11. The medical device of claim 1, wherein the secondtube extends from a first tube end to a second tube end, and the secondcollet comprises a second cap at the second tube end.
 12. The medicaldevice of claim 11, wherein the second cap defines an aperturetherethrough, the tensioner being sized to fit through the aperture. 13.A medical device for implantation in a body vessel, the medical devicehaving a proximal end and extending to a distal end and defining alongitudinal axis therebetween, the medical device comprising: a firstdevice half comprising: a first collet comprising a first tube anddefining a lumen therethrough; and a plurality of struts, each of theplurality of struts comprising a first arm and a second arm connected tothe first arm, each first arm having a first end and extending angledaway from the longitudinal axis to a second end, each second arm havinga third end connected to the second end of the first arm and extendingproximally and substantially parallel to the longitudinal axis to afourth end, a locking element being disposed on at least one first arm,each of the first ends of the first arms being disposed within the lumenof the first tube; a second device half comprising: a second colletcomprising a second tube defining a lumen therethrough; and a pluralityof struts, each of the plurality of struts having a first arm and asecond arm connected to the first arm, each first arm having a first endand extending angled away from the longitudinal axis to a second end,each second arm having a third end connected to the second end of thefirst arm and extending distally and substantially parallel to thelongitudinal axis to a fourth end, a locking element being disposed onat least one first arm, each of the first ends of the first arms beingdisposed within the lumen of the second tube; and a tensioner having afirst end and extending to a second end, the first end of the tensionerbeing attached to the first collet, the tensioner extending to thesecond end through the second collet; wherein the second collet furthercomprises a tensioner-retaining groove for retaining a portion of thetensioner.
 14. The medical device of claim 13 wherein the first devicehalf and the second device half have a conical shape comprising anapical end and an open portion opposite the apical end, the second endsof the first arms being arranged circumferentially about the openportion.
 15. The medical device of claim 14 wherein the first ends ofthe struts of the device halves converge at the apical end of eachconical shape.
 16. The medical device of claim 13 wherein when the firstdevice half and the second device half are moved longitudinallytogether, the locking elements of the first device half contact thelocking elements of the second device half to form a locking interfacesuch that application of a force along a longitudinal axis of the firstdevice half in the distal direction causes the device to exert a forceradially outward therefrom.
 17. A medical device for implantation in abody vessel, the medical device having a proximal end and extending to adistal end and defining a longitudinal axis therebetween, the medicaldevice comprising: a first device half comprising: a first colletcomprising a first tube and defining a lumen therethrough; and aplurality of struts, each of the plurality of struts comprising a firstarm and a second arm connected to the first arm, each first arm having afirst end and extending angled away from the longitudinal axis to asecond end, each second arm having a third end connected to the secondend of the first arm and extending proximally and substantially parallelto the longitudinal axis to a fourth end, a locking element beingdisposed on at least one first arm, each of the first ends of the firstarms being disposed within the lumen of the first tube; a second devicehalf comprising: a second collet comprising a second tube defining alumen therethrough; and a plurality of struts, each of the plurality ofstruts having a first arm and a second arm connected to the first arm,each first arm having a first end and extending angled away from thelongitudinal axis to a second end, each second arm having a third endconnected to the second end of the first arm and extending distally andsubstantially parallel to the longitudinal axis to a fourth end, alocking element being disposed on at least one first arm, each of thefirst ends of the first arms being disposed within the lumen of thesecond tube; and a tensioner having a first end and extending to asecond end, the first end of the tensioner being attached to the firstcollet, the tensioner extending to the second end through the secondcollet; wherein the first tube extends from a first tube end to a secondtube end, the first collet comprises a first cap at the first tube end,and the first end of the tensioner is attached to the first cap.
 18. Themedical device of claim 17 wherein the first device half and the seconddevice half have a conical shape comprising an apical end and an openportion opposite the apical end, the second ends of the first arms beingarranged circumferentially about the open portion.
 19. The medicaldevice of claim 18 wherein the first ends of the struts of the devicehalves converge at the apical end of each conical shape.
 20. The medicaldevice of claim 17 wherein when the first device half and the seconddevice half are moved longitudinally together, the locking elements ofthe first device half contact the locking elements of the second devicehalf to form a locking interface such that application of a force alonga longitudinal axis of the first device half in the distal directioncauses the device to exert a force radially outward therefrom.